Prove the Following by Using the Principle of Mathematical Induction for All N ∈ N: N (N + 1) (N + 5) is a Multiple of 3. - Mathematics

Question

Prove the following by using the principle of mathematical induction for all n ∈ N: n (n + 1) (n + 5) is a multiple of 3.

Solution

Let the given statement be P(n), i.e.,

P(n): n (n + 1) (n + 5), which is a multiple of 3.

It can be noted that P(n) is true for n = 1 since 1 (1 + 1) (1 + 5) = 12, which is a multiple of 3.

Let P(k) be true for some positive integer k, i.e.,

k (k + 1) (k + 5) is a multiple of 3.

∴k (k + 1) (k + 5) = 3m, where m ∈ N … (1)

We shall now prove that P(k + 1) is true whenever P(k) is true.

Consider

Thus, P(k + 1) is true whenever P(k) is true.

Hence, by the principle of mathematical induction, statement P(n) is true for all natural numbers i.e., n.

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Principle of Mathematical Induction

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Q 19 Q 18 Q 20

Chapter 4: Principle of Mathematical Induction - Exercise 4.1 [Page 95]

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NCERT Mathematics [English] Class 11

Chapter 4 Principle of Mathematical Induction
Exercise 4.1 | Q 19 | Page 95

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